Addressing OLTP Solutions with CICS: The Transaction Server ... - Ibm

Figure 38. Combining Resources
122 CICS for AIX as the Transaction Server
In this example we have three separate systems, each with a CICS for AIX
system running a separate application. The application on machine 1 is
approaching the limit of its CPU capacity. Machines 2 and 3 are lightly used. By
restructuring the environment so that each application is available within each
CICS system, you can provide some significant improvements to the service that
users receive when workload management is added to the restructured
environment. Now, each of the three applications is available in each of the
CICS for AIX systems. Thus the work of each of the applications can be split
across the processing power of the three systems. This is most significant for
application 1, as it was approaching the CPU limit of the machine on which it
was running. There is now additional capacity available to it, so it is not
necessary to buy a larger machine for running the application. Applications 2
and 3 have also gained. They have greater availability as they are available on
more systems. In the event of a failure of any of the CICS systems or machines,
all of the applications will still be available to their respective users. The
performance may not be as good as it was before the failures, but the
applications are available, which is the most important consideration.
8.5.1.2 Multiple CICS Systems on One Machine
Although the ideal approach is to be able to combine machines to provide
additional resilience to a workload managed environment, benefit can also be
obtained by providing multiple CICS systems on a single machine. This
approach gives greater availability in the event of a CICS system failure. The
gain is less than it would be with multiple machines, as the work is supported
only on a single machine. An outage of that machine will take both systems
down. Multiple regions on a single machine is not particularly recommended
unless there is the machine processing capacity to cope with it, ideally an SMP.
Adopting such an approach on a uniprocessor would have questionable value as
there would be two regions competing for CPU where previously there had been
one.